The proposed study will give information about the localization, binding and mobility of cholesterol in the human erythrocyte membrane. Abnormal erythrocytes containing excess cholesterol such as the spur cells found in patients with liver disease will be studied to determine whether the excess cholesterol has a distinguishable environment and hence is segregated from the rest of the membrane cholesterol. Kinetic studies of cholesterol movement between abnormal erythrocytes and sonicated phospholipid vesicles will be carried out. X-ray diffraction studies will be made to obtain structural information both about these modified membranes and normal erythrocyte membranes. The affinity of cholesterol for different phospholipids will be determined from a study of the equilibrium distribution of cholesterol between erythrocyte membranes and sonicated phospholipid vesicles.